Consider a database that represents the location of moving objects, such as taxi-cabs typical query: retrieve the cabs that are currently within 1 mile of 33 Michigan Ave., Chicago, or objects in a battle-eld. Existing database management systems DBMS's are not well equipped to handle continuously changing data, such as the position of moving objects, since data is assumed t o b e c onstant unless it is explicitly modied.In this paper we address position-update policies and imprecision. Namely, assuming that the actual position of a moving object m deviates from the position computed by the DBMS, when should m update its position in the database in order to eliminate the deviation? Furthermore, how can the DBMS provide a bound on the error i.e. the deviation when it replies to a query: what is the current position of m? We propose a cost based approach to update policies that answers both questions. We develop several update policies and analyze them theoretically and experimentally.
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